1. Field
Aspects of the present invention relate to an image forming apparatus in an electrophotographic method and to a fuser of the image forming apparatus, and more particularly to an image forming apparatus equipped with a fuser in a belt fixing method.
2. Description of the Related Art
In general, an image forming apparatus in an electrophotographic method includes an image supporting body structured so that a developing agent such as toner can be supported, a transfer member that transfers the developing agent supported on the image supporting body to a recording sheet, and a fuser that thermally fixes the developing agent transferred to the recording sheet. In a known method used by a fuser, an endless belt (fixing film) is held between a nip member placed so as to face the inner surface of the belt and a rotating body (pressurizing roller) placed so as to face the outer surface of the belt, after which the developing agent is heated to melt it and the melted developing agent is fixed on the recording sheet in a process in which the recording sheet on which the developing agent is supported is conveyed while being held between the belt and the rotating body.
As for a fuser based on this method, a structure is known in which fluid guide grooves are formed in a surface, of the nip member, that is in contact with the belt to evenly distribute a lubricant used to enhance slidability between the nip member and the belt.
Because of design considerations for a recording sheet conveying path in the image forming apparatus, the nip member and rotating body are placed so that the contact portion of the nip member faces downward as in Japanese Unexamined Patent Application Publication No. 2008-146964. In addition to this aspect, an aspect in which the contact portion of the nip member is oriented at an angle as indicated in FIG. 1 in U.S. patent publication no. 2009/0175645 has been practiced.
In the structure described in Japanese Unexamined Patent Application Publication No. 2008-146964, a lubricant can be evenly distributed on the contact portion of the nip member, but there is no consideration for the lubricant flowing outwardly from the contact portion. If the lubricant flows outwardly from the contact portion, the lubricant may proceed along the smooth surface of the nip member and may turn back and enter the back of the nip member. As a result, the lubricant may contaminate the interior of the apparatus. In addition, if the amount of lubricant is reduced due to its outward flow, the slidability of the belt may be reduced. Then, the driving torque of the belt may be increased and the belt becomes more likely to slip. Furthermore, the apparatus may be deteriorated earlier than expected.
Particularly in the structure described in U.S. patent application No. 2009/0175645, in which the contact portion of the nip member is oriented at an angle, if the lubricant overflows from the contact portion of the nip member and enters the interior of the fusing device from the downstream end of the nip member, the lubricant may contaminate a heating element, a reflecting plate, which reflects radiant heat from the heating element, and other components in the fuser. This may lower the performance of the fuser.
Noting the issue of suppressing a lubricant from flowing out from the upwardly oriented contact portions of the nip member and other members in a fuser, particularly from the downstream end of the contact portion in a direction in which a recording sheet is conveyed (belt sliding direction), the inventors of this application repeated diligent study and devised the present invention.